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The Effects of Cluster Thinning on Vine Performance, Fruit, and Wine Composition of Pinot Noir (Clone 115) in the Edna Valley of CaliforniaMawdsley, Paul F W 01 September 2019 (has links)
A three-year study was conducted at a commercial vineyard site in California’s Edna Valley AVA to evaluate the physiological and agronomical effects of the timing of cluster thinning on Pinot noir (clone 115) grapevines. Vines were thinned to one cluster per shoot at three selected time-points during the growing season (bloom, bloom + 4 weeks, bloom + 8 weeks), and fruit from each treatment was harvested and made into wine. Across all growing seasons, yield decreased 43% in thinned vines relative to un-thinned control vines. No effect of cluster thinning or interaction with growing season was found in vine shoot diameter, internode length, fruit zone light level, or cluster weight. Growing season significantly affected more fruit and wine parameters than did cluster thinning treatment, with interactions between treatment and growing season found in fruit Brix, titratable acidity, and anthocyanins, as well as wine anthocyanins and wine b* (yellow component). For example, bloom + 8 and bloom + 12 thinning treatments advanced Brix in 2017 but had no effect in 2018. Cluster thinning treatments increased berry anthocyanins by 43% in 2017 and by 103% in 2018 relative to the control. Similarly, cluster thinning increased berry total phenolics by 87% in 2017 and by 140% in 2018 relative to the control, with no significant differences found between the different thinning treatments. However, the levels of anthocyanins and total phenolics were generally not affected by cluster thinning treatment in the resulting wines. The fact that different cluster thinning treatments resulted in nil or minor effects on fruit and wine suggests that the vines tested were at or below a balanced crop load prior to the application of cluster thinning. Edna Valley AVA could likely support higher crop loads than 3.2 on the Ravaz index without negatively impacting fruit or wine composition and reducing crop load below that level is unlikely to increase fruit or wine quality.
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Non-destructive assessment of leaf composition as related to growth of the grapevine (Vitis vinifera L. cv. Shiraz)Strever, Albert (Albert Erasmus) 03 1900 (has links)
Thesis (PhD(Agric))--Stellenbosch University, 2012 / ENGLISH ABSTRACT: Field spectroscopy was used to study leaf composition and selected factors (including canopy
growth manipulation and water status changes) that may impact on it in a Vitis vinifera cv. Shiraz
vineyard, showing considerable variability in vigour. Temporal and spatial variability in leaf
composition were incorporated into measurements by analysing leaves in different shoot positions
and at different developmental stages during three different growing seasons. Irrigation and
canopy manipulation treatments were also imposed in order to provide new insights into assessing
the grapevine leaf and possibly also the canopy growth and ageing dynamics as well as pigment
content, as a basis of executing a generally non-destructive measurement approach.
Despite large climatic differences between the seasons, canopy size seemed of crucial importance
in determining grapevine water relations in the grapevines from the different canopy manipulation
treatments. Drastic compensation effects in terms of secondary shoot growth also followed the
canopy reduction treatment. Despite this, canopy microclimate was apparently improved,
considering the results from light measurements as well as the ripening dynamics in the reduced
canopies. Reduced canopies also seemed to display a different canopy composition, in favour of
secondary growth. This could have impacted positively on water use efficiency as well as ripening,
due to higher photosynthetic efficiency of these leaves during the ripening stages. The reduced
canopy treatments offered the possibility of attaining technological ripeness at an earlier stage and
at comparatively lower potential alcohol levels.
This study illustrated the relevance of considering the vegetative development of the grapevine,
along with leaf ageing in the canopy, when conducting calibrated non-destructive measurements of
leaf pigments, structure and water content. The relevance of using multivariate techniques in leaf
spectroscopy was shown. This can be applied and simplified to aid in non-destructive leaf pigment,
structure and water content estimation in future studies. Even with the general variation
encountered in this vineyard, predictions of the major pigments in grapevine leaves were within
acceptable error margins. Further work is required to improve the modelling of xanthophylls, which
may require non-linear multivariate techniques.
Logistical shoot growth modelling was used in leaf age estimation and classification, which made it
possible to simplify statistical analysis of the leaf parameters mentioned. Practical application of
the modelled and predicted parameters was shown for a specific period in season two by
comparing the reaction of different treatments to developing water deficits. The results indicated
that several parameters, with special mention of the carotenoid:chlorophyll ratio and chlorophyll a:b
ratio, can be monitored on young and old leaves in the canopy in order to monitor developing water
deficit stress. The modelled parameters, however, did not seem to be sensitive enough to allow
specific prediction of predawn leaf water potential values. Specific leaf mass, equivalent water
thickness, total specific leaf mass as well as leaf chronological age were successfully predicted
from leaf spectral absorbance data, and this may be useful in future work on quantifying leaf
adaptation to the micro-environment within the canopy. / AFRIKAANSE OPSOMMING: Veldspektroskopie is gebruik om blaarsamestelling en spesifieke faktore (insluitend lowergroei
manipulasie en waterstatus veranderinge) wat ‘n impak kan hê in ‘n Vitis vinifera cv. Shiraz
wingerd, met beduidende variasie in groeikrag, te ondersoek. Ruimtelike, asook tydsgebonde,
variasie in blaarsamestelling is geïnkorporeer in die metings deur blare van verskillende
lootposisies en vir verskillende ontwikkelingstadia gedurende drie verskillende groeiseisoene te
meet. Besproeiings- en lowermanipulasie behandelings is ook uitgevoer om die dinamiek van
blaar- en lowergroei, veroudering, asook pigmentinhoud te bestudeer binne die konteks van die
uitvoering van ‘n nie-destruktiewe meetstrategie.
Ondanks groot klimaatsverskille tussen die seisoene, blyk lowergrootteverskille belangrik te wees
in die bepaling van wingerdstok-waterverhoudings in die verskillende lowermanipulasie
behandelings. Drastiese kompensasiereaksies ten opsigte van sylootgroei is waargeneem in
reaksie op die gereduseerde lowerbehandeling. Indien die resultate van ligmetings en
druifrypwording in die gereduseerde lowerbehandeling in ag geneem word, is lowermikroklimaat
egter steeds verbeter. Hierdie behandeling het oënskynlik ook veranderde lowersamestelling
gehad, tot voordeel van sylootgroei. Dit kon moontlik ‘n positiewe invloed gehad het op
waterverbruikseffektiwiteit asook druifrypwording, as gevolg van moontlike hoër fotosintetiese
effektiwiteit van die blare gedurende die rypwordingstadia. Die gereduseerde lowerbehandeling het
die moontlikheid gebied om tegnologiese rypheid by ‘n vroeër datum te bereik, met moontlike laer
alkoholvlakke in die wyn.
Hierdie studie het die belangrikheid beklemtoon om die vegetatiewe ontwikkeling van die
wingerdstok in ag te neem wanneer gekalibreerde nie-destruktiewe metings van blaarpigmente,
blaarstruktuur asook waterinhoud onderneem word. Die belang van multi-variant meettegnieke in
blaarspektroskopie is aangetoon. Dit kan verder vereenvoudig word ter ondersteuning van niedestruktiewe
meting van blaarpigment, -struktuur en -waterinhoudsbepaling in toekomstige studies.
Selfs met die variasie wat in die wingerd voorgekom het, was die voorspellings van die vlakke van
die belangrikste pigmente wat in wingerdblare aangetref word binne aanvaanbare foutgrense.
Opvolgwerk is nodig om die modellering van xanthofil te verbeter, aangesien dit moontlik nielineêre
multi-variant analise mag benodig.
Logistiese groeimodellering is gebruik om blaarouderdom te bepaal en te klassifiseer, wat dit
moontlik gemaak het om statistiese analise te vereenvoudig vir die genoemde blaarparameters.
Die praktiese toepassing van die gemodelleerde en voorspelde parameters is aangetoon vir ‘n
spesifieke gedeelte in seisoen twee, deur die reaksie van verskillende behandelings op
toenemende watertekorte te bestudeer. Resultate het aangetoon dat verskeie parameters, met
spesifieke klem op die karotenoïed:chlorofil verhouding, asook die chlorofil a:b verhouding,
gemoniteer kan word op jong en ouer blare in die lower ten einde ontwikkelende
waterstrestoestande te identifiseer. Die gemodelleerde parameters was egter klaarblyklik nie
sensitief genoeg vir akkurate voorspelling van voorsonsopkoms-waterpotensiaalvlakke nie.
Spesifieke blaarmassa, ekwivalente waterdikte, totale spesifieke blaarmassa, sowel as
blaarouderdom kon suksesvol voorspel word deur gebruik te maak van absorpsieblaarspektroskopie,
wat nuttig kan wees in toekomstige studies wat handel oor die kwantifisering
van blaaraanpassing by die mikro-omgewing binne ‘n wingerdlower.
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Effect of varying levels of nitrogen, potassium and calcium nutrition on table grape vine physiology and berry qualityRaath, P. J. ( Pieter Johannes) 03 1900 (has links)
Thesis (PhD(Agric))--Stellenbosch University, 2012. / ENGLISH ABSTRACT: A lack of defects is required for successful table grape marketing, which pre-suppose
optimal vine performance, berry development and post-harvest quality. The supply of
mineral nutrients affects vine development, physiology and berry quality. Despite a vast
amount of research conducted over decades, there remain many unresolved issues
regarding table grape vine nutrition to ensure optimal table grape quality and shelve-life.
Unjustified fertilisation practices often include excessive applications of nitrogen (N),
potassium (K) and calcium (Ca).
A four-year field trial was therefore conducted on a sandy soil in the Paarl district of South
Africa, using grafted on Ramsey, and trained to a gable trellis system. Nitrogen, potassium
and calcium were applied, singular or in combination, at rates up to 300% the calculated
annual nutritional requirement. The effect of these excessive applications on table grape
performance under typical South African cultivation conditions was investigated for Vitis
vinifera L. cv. Prime Seedless, a very early seedless table cultivar that is produced with
minimum berry diameter of 18mm, with special reference to 1) vegetative growth, 2)
expression of grapevine nutrient availability through foliar analyses, 3) berry nutrient
accumulation patterns of this early cultivar, 4) manipulation of berry nutrient content through
soil and bunch directed applications and 5) the effect of berry nutrient content on its quality.
No definite vegetative growth responses (expressed as shoot length, leaf surface area and
shoot mass) and leaf chlorophyll content differences were obtained for all the treatments.
These results were obtained in a vineyard on a sandy soil where excessive N fertilisation
caused a reduction of soil pH to detrimentally low levels and where the excessive N, K and
Ca applications reduced mutual concentrations and that of Mg, in the soil. A lack of
stimulation in vegetative growth may therefore be ascribed to the combined negative effect
of these excessive applications on soil pH and vine nutrition.
Although the N content of petioles was higher for treatments where N was applied,
consistent significant increases in petiole N with N fertilisation were not observed. Petiole N
concentration showed a decreasing trend throughout the season. Petiole K concentrations
were significantly increased by the K fertilisation at all phenological stages. None of the K
fertilisation treatments, however, succeeded to raise petiole K concentrations above the
accepted maximum norms and petiole K concentration at a specific sampling stage varied
significantly between the four seasons. A general decrease in petiole K concentration was found for all seasons. Calcium fertilisation did not increase soil Ca content, resulting in a
lack of differences in petiole Ca concentrations between treatments. An increase in petiole
Ca concentration towards harvest was obtained. Correlations between petiole nutrient
concentration and berry mineral content at harvest were poor. The only way of knowing the
mineral content of berries would seem to be by measuring it directly instead of deducing it
from the results of leaf or petiole analyses.
The dynamics of berry growth impacted on berry nutrient concentration. Early rapid berry
growth, predominantly due to cell division and cell growth, was associated with the most
rapid decreases in N, P and Ca concentration. Due to mobility of K and Mg in the plant, that
exceeds other nutrients, the decrease in concentration of these two mineral elements was
not as pronounced as that of the others. Nutrient accumulation was most rapid during the
pre-véraison period, but only Ca showed a definite termination during the early ripening
period. The continued inflow of N, P, K and Mg, albeit at slower rates immediately after
véraison, should be taken into consideration when fertilisation is applied. As a table grape,
total accumulation of each nutrient in Prime Seedless berries also far exceeded that of
other cultivars studied thus far. A particular difference is that the berry flesh:skin ratio is
much higher than that of previously studied cultivars, leading to higher levels of nutrient
accumulation in the flesh.
Slightly larger berry size was obtained for N applications and is ascribed to slight increases
in early vegetative growth, allowing a better response to GA3 treatments. The use of GA3 for
berry enlargement is also considered the reason why K fertilisation, resulting in increased
berry K levels, did not affect berry size, as is often found for wine grapes.
Higher available NO3
- in the soil on account of excessive N applications resulted in higher
levels of berry N, despite sub-optimal soil pH regimes that were created by these
treatments.
Berry K concentration and content were increased by K fertilisation. Rapid vine K uptake
and translocation to the berries seem to negate the reduced vine nutritional status as
observed in petioles for situations of over-fertilisation with N. Berry Ca levels were not
increased by Ca fertilisation or by bunch applied Ca. The rapid rates of berry growth,
together with low rates of berry Ca uptake and Ca uptake that terminates at the onset of
ripening, are assumed to be the main reasons for this result.
Low levels of decay as well as a lack of consistently increased decay were obtained for N
containing treatments. Nitrogen levels in the berries above which their susceptibility to
fungal infection is increased, should be established. Information on specific N compounds
that may lead to more susceptibility is required. Potentially increased berry browning on
account of high rates of K fertilisation needs to be further investigated; indications that this
may occur were observed. Neither soil applied Ca nor bunch applied Ca improved berry
quality, although Ca treatments seemed to reduce decay during the only season that
significant differences were obtained.
The negative effect of excessive fertilisation on soil chemistry of sandy soils has again been
highlighted by this study. This annuls the fertilisation, leading to inefficient fertilisation and a
lack of the desired responses.
As indicator of vine nutrient availability, petiole analysis, was proven unreliable and should
be evaluated in parallel with soil analyses, taking seasonal variation into consideration. The
danger of being only guided by published norms for leaf nutrient concentrations when
establishing fertilisation practices has again been highlighted by this study.
This research indicated that for a very early cultivar like Prime Seedless, nutrient
accumulation dynamics can already start to change during the pre-véraison period in some
seasons. This is due to different edaphic and climatic conditions as well as berry size,
which leads to much higher flesh:skin ratios. Future research on table grapes would need to
develop an understanding of the various factors and dynamics that determine berry nutrient
concentration and accumulation of early ripening, large berry sized, seedless table grape
cultivars. / AFRIKAANSE OPSOMMING: Suksesvolle bemarking van tafeldruiwe is ten nouste afhanklik van die beskikbaarheid van
druiwe sonder defekte, wat ‘n direkte verband met optimale wingerdprestasie,
korrelontwikkeling en na-oes kwaliteit inhou. Voorsiening van minerale voedingstowwe
beïnvloed die stok se groei, fisiologie en korrelgehalte. Ten spyte van ‘n oorweldigende
hoeveelheid navorsing wat oor dekades reeds gedoen is, is daar steeds onopgeloste
kwessies aangaande bemesting van tafeldruiwe vir optimale druifgehalte en houvermoë.
Die gevolg is onoordeelkundige bemestingspraktyke wat o.a. aanleiding gee tot
oorbemesting met stikstof (N), kalium (K) en kalsium (Ca).
‘n Vier-jaar-lange veldproef is gevolglik op ‘n sandgrond in die Paarl distrik (Suid-Afrika)
onderneem deur gebruik te maak van Vitis vinifera L. cv. Prime Seedless geënt op Ramsey
en op ‘n dubbel-gewel prieelstelsel opgelei is. Stikstof, K en Ca is alleen, of in kombinasie,
toegedien teen hoeveelhede gelykstaande aan 300% van die wingerd se jaarlikse behoefte.
Die effek van hierdie oormatige toedienings op tafeldruif prestasie onder Suid-Afrikaanse
verbouingstoestande is ondersoek, met spesiale verwysing na 1) vegetatiewe groei, 2)
uitdrukking van voedingstofbeskikbaarheid deur blaarontledings, 3) die voedingstof
akkumulasie patrone van korrels van hierdie vroeë kultivar, 4) manipulasie van korrel
voedingstofinhoud deur grond en trosgerigte toedienings en 5) die effek van korrel
voedingstofinhoud op kwaliteit.
Die doel van die proef was om bemestinspraktyke van Prime Seedless, ‘n baie vroeë
pitlose tafeldruifkultivar met ‘n minimum korrelgrootte van 18 mm, te verfyn. Deur die
akkumulasie patrone van die druiwe uit te klaar is daar ook ondersoek ingestel of oestyd en
na-oes gehalte deur oormatige toediening van voedingstowwe affekteer word.
Geen duidelike verskille betreffende vegetatiewe groeireaksies (uitgedruk as lootlengte,
blaaroppervlaktes en lootmassas) asook verskille in blaar chlorofilinhoud is vir die
behandelings verkry nie. Hierdie resultate is verkry in ‘n wingerd op ‘n sandgrond, waar
oormatige N-bemesting aanleiding gegee het tot grond pH verlagings tot die peil van
nadelige vlakke. Verder het die oormatige N, K en Ca toedienings wederkerige verlagings
in konsentrasies, asook op dié van Mg, in die grond teweeggebring. Die tekort aan
vegetatiewe groeiresponse op die behandelings kon dus toegeskryf word aan ‘n
gekombineerde effek van die oormatige toedienings op grond pH en voedingstofbalanse.
Hoewel die N-inhoud van bladstele hoër was vir behandelings wat N toediening ingesluit
het, was daar nie konstante toenames in die vlakke verkry nie. Bladskyf N-konsentrasie het
afgeneem deur die loop van die groeiseisoen. Vir alle fenologiese stadiums was bladskyf Kkonsentrasies
betekenisvol verhoog deur K-bemesting. Nie een van die Kbemestingsbehandelings
het egter daarin geslaag om bladskyf K inhoud vir enige
monstertyd bo die algemeen aanvaarde maksimum norms te lig nie. Verder het bladskyf K
inhoud by ‘n spesifieke fenologiese stadium ook betekenisvol tussen seisoene verskil. Die
K-inhoud van bladskywe het afgeneem met verloop van die seisoen. Kalsiumbemesting
het nie die grond se Ca inhoud deurgans verhoog nie, wat dus die tekort aan verskille in Ca
konsentrasies tussen die behandelings verklaar. ‘n Toename in Ca konsentrasie en korrel
Ca inhoud is vanaf set tot oes waargeneem. Swak korrelasies tussen bladskywe se
voedingstofinhoude en korrels se voedingstofinhoude is verkry. Die enigste manier waarop
korrels se voedingstofinhoude dus afgelei kan word, blyk te wees deur direkte bepaling
daarvan.
Voedingstofinhoude van korrels is deur groeipatrone daarvan beïnvloed. Vroeë korrelgroei,
hoofsaaklik a.g.v. seldeling en selgroei, het met die vinnigste afnametempo van N, P en Ca
gepaard gegaan. As gevolg van die hoër beweeglikheid van K en Mg in die plant in
vergelyking met ander voedingstowwe, was die afname in konsentrasie van hierdie twee
elemente nie so groot soos vir die ander nie. Voedingstofakkumulasie was die vinnigste in
die periode voor deurslaan. Slegs Ca het ‘n beeïndiging van opname aan die einde van
hierdie periode getoon. Die voortgesette opname van N, P, K en Mg, alhoewel stadiger kort
na deurslaan, moet in ag geneem word wanneer bemesting toegedien word. Vir hierdie
kultivar het die totale opname van elke bemestingstof dié van die ander kultivars wat tot
hede bestudeer is, ver oorskry. ‘n Spesifieke verskil is ‘n baie hoër vleis:dop verhouding as
wat vir ander kultivars verkry is. Dit gee aanleiding tot baie hoër vlakke van
voedingstofakkumulasie in die vleis.
Effens groter korrelgroottes is verkry waar N toedienings gemaak is. Dit word toegeskryf
aan klein toenames in vroeë vegetatiewe groei, wat dus beter reaksie op GA3 behandelings
tot gevolg gehad het. Die gebruik van GA3 vir korrelvergroting word ook beskou as die rede
waarom K-bemesting, wat tot hoër vlakke van K in die korrels aanleiding gegee het, nie
korrelgrootte, soos by wyndruiwe, bevorder het nie.
Hoër NO3
- in die grond (water), na aanleiding van N toedienings, het aanleiding gegee tot
hoer vlakke van N in die korrels. Dit het plaasgevind ten spyte van sub-optimale grond pH
wat deur die oormatige N toedienings veroorsaak is.
Korrel K konsentrasie en -inhoud is deur K-bemesting verhoog. Vinnige opname en
translokasie van K na die korrels het ook geblyk die rede te wees waarom die verlaagde
voedingstatus van die stokke a.g.v. oorbemesting met N nie die korrels se K inhoud
geaffekteer het nie. Die vinnige groeitempo van die korrels, tesame met lae vlakke van Ca
opname, asook korrels se Ca opname wat tydens rypwording ophou, word as die redes vir
die tekorte aan behandelingseffekte beskou.
Lae vlakke van bederf, asook ‘n tekort aan betroubare tendense dat bederf deur Nbemesting
verhoog word, is verkry. Daar moet vasgestel word of daar N vlakke in die
korrels is waarbo hul vatbaarheid vir swaminfeksies verhoog word, en of daar spesifieke N
verbindings is wat die korrels meer vatbaar maak vir bederf. Indikasies dat K-bemesting
interne verbruiningsvlakke verhoog het, regverdig verdere ondersoek. Korrelkwaliteit is nie
deur grond- of trosgerigte toedienings bevoordeel nie.
Die negatiewe effek van oormatige bemesting op die chemiese samestelling van
sandgronde is weer deur hierdie navorsing uitgelig. Dit lei tot oneffektiewe bemesting en ‘n
tekort aan die verlangde effekte.
Blaarontledings blyk onbetroubaar te wees as aanduiding van voedingstof beskikbaarheid.
Dit moet evalueer word saam met grondontledings en ook seisoenale variasie in ag neem.
Die gevaar om slegs deur gepubliseerde norme gelei te word wanneer bemestingspraktyke
bepaal word, is weer deur hierdie navorsing uitgelig.
Voorst is daar in hierdie navorsing gevind dat voedingstof akkumulasiepatrone van ‘n baie
vroeë kultivar soos Prime Seedless alreeds voor deurslaan begin verander a.g.v.
omgewingstoestande en korrelgroei wat tot ‘n veel hoër vleis:dop verhouding aanleiding
gee. Toekomstige navorsing op tafeldruiwe behoort die faktore en dinamika wat
voedingstofkonsentrasie en -akkumulasie in korrels van vroeë, groot korrel, pitlose
tafeldruifkultivars beïnvloed verder te ondersoek.
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Factors influencing the fermentation performance of commercial wine yeastsFerreira, Jacques 12 1900 (has links)
Thesis (MScAgric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The production of quality wine is influenced by numerous factors of which grape
quality is one of the most important factors. The production of quality wine, however,
is not possible without good winemaking techniques and effective quality control.
Critical control points (CCP) during the winemaking process must be identified to
ensure optimum wine quality. Grape must is a complex medium that contains
different micro-organisms which can be either beneficial or negative to wine quality,
depending on the physical and chemical conditions that prevail in the must. Yeasts
are responsible for alcoholic fermentation, lactic acid bacteria (LAB) for malolactic
fermentation (MLF) and acetic acid bacteria (AAB) for the production acetic acid from
ethanol. Yeasts and certain LAB can also produce acetic acid and thereby increasing
the volatile acidity (VA) of wine. These micro-organisms can influence each other in
complex fashions by competing for growth nutrients and by producing inhibitory
substances.
Most winemakers nowadays use commercial yeast strains to inoculate wine
fermentations. This, however, does not assure a problem-free fermentation and
cases of stuck and sluggish fermentations are annually reported worldwide. In these
or most cases fermentation takes longer than 21 days to complete and the wine
contains a residual sugar concentration of more than 4 g/L, which can be utilised by
wine spoilage micro-organisms such as certain bacteria and other wild yeasts. Stuck
and sluggish fermentations also increase the chances of oxidation due to the
absence of the protective CO2 layer on the surface of the wine, which is formed
during alcoholic fermentation. Another effect of stuck and sluggish fermentations is
that valuable tank space is wasted due to the unexpected time consumption of these
fermentation problems. Many factors during the winemaking process can be
responsible for stuck and sluggish fermentations. In this thesis the different factors is
discussed with the emphasis on the effect of the yeast strain. The way that certain
yeast strains influence AAB and LAB numbers during fermentation and MLF through
the production of inhibiting by-products such as medium chain fatty acids has not
been investigated in detail in the past.
Certain fungicides and pesticides that are used in vineyards to control pests (e.g.
mildew) contain copper which can be inhibiting to yeast growth and alcoholic
fermentation. Legal limits and withholding periods on these sprays are not always
strictly obeyed and can lead to stuck and sluggish fermentations. This motivated us
to evaluate the growth and fermentation activities of a selection of commercial wine
yeasts in the presence of copper levels in the range of maximum legal limits. The
effect of these commercial strains on the LAB and AAB numbers during alcoholic
fermentation and MLF were also investigated.
Our results showed that there was no significant difference on numbers of the
AAB obtained from fermentations inoculated with different commercial wine yeast strains. However, with regards to the LAB numbers, one of the strains produced
significantly more sulphur dioxide (SO2), which led to the inhibition of MLF in that
wine. Our results further indicated which commercial yeast strains were capable of
effectively fermenting high sugar musts and which strains were less effective. From
the strains tested VIN13, N96 & L2056 were able to utilize fructose more effectively
than NT50, RJ11 & D80. We could further distinguish between yeast strains that
produced the lowest (VIN13 & RJ11) and the highest (WE372, NT50 & L2056) VA
concentrations in must containing high sugar levels. Strains that were more tolerant
against high copper levels were also identified. We tested six yeast strains in must
with added copper (0.25 mM cu2+) in the form of CuSO4
.H2O. Three Cu2+-tolerant
(D80, Collection Cepage Cabernet & NT50) yeast strains were distinguished from
three less Cu2+-tolerant yeast strains (VIN13, NT112 & RJ11).
This study made a valuable contribution in knowledge gained about commercially
available wine yeast strains that can ferment effectively under certain stress
conditions. Research such as this, where wine yeasts are evaluated to ferment more
effectively during strenuous winemaking conditions, will be very beneficial to
winemakers. / AFRIKAANSE OPSOMMING: Die produksie van gehalte wyn word deur verskillende faktore beïnvloed waarvan
druifkwaliteit seker die belangrikste is. Die produksie van gehalte wyn is egter nie
moontlik sonder goeie wynmaaktegnieke en effektiewe kwaliteitsbeheer nie. Kritieke
kontrole punte (KKP) tydens die wynmaakproses moet dus geïdentifiseer word om
sodoende ‘n verlaging in wynkwaliteit te vermy. Druiwemos het ‘n komplekse
mikrobiologiese samestelling en bestaan uit verskillende mikroörganismes wat vooren
nadelig vir wynkwaliteit kan wees, afhangende van die fisiese en chemiese
toestande wat in die mos bestaan. Giste is verantwoordelik vir alkoholiese
fermentasie, melksuurbakterieë (MSB) vir appelmelksuurgisting (AMG) en
asynsuurbakterieë (ASB) vir die produksie van asynsuur vanaf etanol. Asynsuur word
egter ook deur giste en MSB geproduseer en dra so by tot die vlugtige suurheid (VS)
van ‘n wyn. Hierdie mikroörganismes kan mekaar op komplekse wyses beïnvloed
deur o.a. te kompeteer vir voedingstowwe asook deur die produksie van inhiberende
verbindings.
Die meeste wynmakers maak gebruik van kommersiële gisrasse om alkoholiese
fermentasies mee uit te voer. Gevalle van sogenaamde slepende en gestaakte
alkoholiese fermentasies, waar suiker nie volledig na etanol en CO2 omgeskakel
word nie, kom egter nog gereeld in die wynbedryf voor. In sulke gevalle neem die
fermentasie gewoonlik langer as 21 dae om te voltooi met ‘n suiker konsentrasie van
meer as 4 g/L wat in die wyn oorbly. Dit is nadelig vir wynkwaliteit aangesien dit nie
net die kanse vir bederf deur bakterieë en giste verhoog nie, maar ook die kanse vir
oksidasie verhoog a.g.v. die verlies van die beskermende CO2 lagie bo-oor die wyn.
Hoe sekere gisrasse, ASB en MSB getalle gedurende fermentasie en AMG
beïnvloed deur die produksie van inhiberende verbindings soos medium ketting
vetsure en SO2, is ook nie baie in die verlede ondersoek nie.
Sommige spuitstowwe wat gebruik word in die bekamping van swamsiektes
bevat koper wat inhiberend kan wees vir gisgroei en alkoholiese fermentasie. Wetlike
maksimum limiete en onthoudingsperiodes op spuitstofresidue word egter nie altyd
gehoorsaam nie en kan lei tot slepende en gestaakte fermentasies. Dit het ons
gemotiveer om ‘n seleksie van kommersiële gisrasse te evalueer in terme van
gisgroei en fermentasie in die teenwoordigheid van kopervlakke naby die maksimum
limiet.
Ons resultate het gewys dat daar nie noemenswaardige verskille in AAB getalle
tydens alkoholiese fermentasie tussen behandelings met verskillende kommersiële
gisrasse was nie. Een van die gisrasse het wel noemenswaardig meer SO2
geproduseer wat gelei het tot inhibering van AMG in hierdie wyn. Ons het verder
uitgewys watter kommersiële gisrasse instaat is om meer effektief in hoër suiker mos
te fermenteer en watter van die rasse minder suksesvol was. Ons het ook rasse
geïdentifiseer wat meer weerstandbiedend is teen hoë kopervlakke in mos en
sodoende groter kans op ‘n suksesvolle fermentasie sal hê in mos wat koperresidue bevat wat afkomstig is van sekere spuitstowwe. Die effek van die ASB en MSB
getalle gedurende fermentasie en AMG is ook ondersoek. Ons resultate het verder
gewys watter kommersiële gisrasse instaat was om mos met hoë suikervlakke meer
effektief te fermenteer. Vam die gisrasse wat getoets was het VIN13, N96 & L2056
fruktose meer effektief benut as NT50, RJ11 & D80. Ons kon verder onderskei
tussen gisrasse wat die laagste (VIN13 & RJ11) en die hoogste (WE372, NT50 &
L2056) vlakke van VS produseer in mos met hoë inisiële suikervlakke. Gisrasse wat
meer tolerant was teen koperresidue in mos is ook geidentifiseer. Ons het ses
gisrasse getoets in mos met bygevoegde koper (0.25 mM Cu2+) in die vorm van
CuSO4
.5H2O. Daar is onderskei tussen drie Cu2+-tolerante (D80, Collection Cepage
Cabernet & NT50) en drie minder Cu2+-tolerante gisrasse (VIN13, NT112 & RJ11).
Hierdie studie lewer ‘n waardevolle bydrae in die invordering van kennis oor
kommersieel beskikbare wyngisrasse wat meer effektief sal fermenteer onder sekere
streskondisies wat in mos voorkom. Inligting soos hierdie is belangrik om die
wynmaker se keuse uit die reeks bestaande kommersiële gisrasse te vergemaklik.
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15 |
The effect of atmospheric and soil conditions on the grapevine water statusLaker, Mareli S. (Mareli Susan) 12 1900 (has links)
Thesis (MScAgric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: Due to the extraordinary drought resistance of the grapevine, viticulture without
irrigation in the winter rainfall coastal areas of South Africa is a feasible and
commonly used practice. Wine quality is largely determined by the quality of the
grapes from which it is made. Grapevine physiology is affected both directly and
indirectly by water stress, which may vary according to soil type and prevailing
atmospheric conditions. The water status of the grapevine can affect grape
composition profoundly, either directly or indirectly, in either a positive or negative
way, depending on the degree as well as the duration of water stress. There are
three important factors involved in the development of water stress, namely the
transpiration rate, the rate of water movement from the soil to the roots, and the
relationship of soil water potential to leaf water potential. All three these factors are
affected by atmospheric and/or soil conditions.
In warm winelands such as South Africa (Western Cape), with a mediterranean
climate which is characterised by a hot, dry summer period, the most important
characteristic of soil is its ability to supply sufficient water to the grapevine during the
entire growing season. Leaf water potential (Ψl) has gained wide acceptance as a
fundamental measure of grapevine water status, and has been widely applied in
viticultural research. Shortly before dawn, Ψl approaches equilibrium with soil water
potential and reaches a maximum daily value.
The study formed an integral part of a comprehensive, multi-disciplinary research
project (ARC Infruitec-Nietvoorbij Project No. WW13/01) on the effect of soil and
climate on wine quality, which commenced in 1993 and will be completed in 2004.
This study was conducted during the 2002/03 growing season in two Sauvignon
blanc vineyards situated at Helshoogte and Papegaaiberg, both in the Stellenbosch
district, approximately nine kilometres apart. Two experiment plots, representing
contrasting soil types in terms of soil water regime, were selected in each vineyard.
At Helshoogte the two soils represented the Tukulu and Hutton forms, and the soils
at Papegaaiberg were of the Avalon and Tukulu forms.
The aim of this study was to determine the effect of atmospheric conditions and
soil water status on the level of water stress in the grapevines for each soil at each
locality, as well as the effect of grapevine water stress on yield and wine quality. This
was done by determining and comparing the soil water status, soil water holding
capacity of the soils and the evapotranspiration of the grapevines on the two different
soils, at each of the two localities differing in mesoclimate and topography. The
atmospheric conditions at the two localities during the 2002/03 season were also
determined and compared to the long-term average atmospheric conditions, and the
level of water stress of grapevines on each soil at each locality was measured. During the 2002/03 growing season, atmospheric conditions were relatively warm
and dry in comparison to the long-term averages of previous seasons. These
conditions accentuated the effects of certain soil properties that may not come
forward during wetter, normal seasons.
The usually wet Tukulu soil at Helshoogte was drier than expected during the
2002/03 season compared to the Hutton soil. Due to more vigorous growth on the
Tukulu soil, grapevines extracted more soil water early in the season, leading to a
low soil water matric potential and more water stress in the grapevines. Due to the
higher vigour, resulting in more canopy shading, and more water stress, the dominant
aroma in wines from the Tukulu soil was fresh vegetative. The Hutton soil maintained
consistency with regards to both yield and wine quality compared to previous
seasons. On the other hand the Tukulu soil supported a higher yield, but with lower
than normal wine quality.
The Avalon soil at Papegaaiberg maintained the highest soil water potential
towards the end of the season, probably due to capillary supplementation from the
sub-soil. Grapevines on the Tukulu soil at Papegaaiberg experienced much higher
water stress than ones on the other three soils, especially during the later part of the
season. This could be ascribed to a combination of factors, the most important being
the severe soil compaction at a shallow depth, seriously limiting rooting depth and
root distribution, which is detrimental to grapevine performance.
Both the soil water status and atmospheric conditions played important roles in
determining the amount of water stress that the grapevines experienced at different
stages. The air temperature and vapour pressure deficit throughout the season were
consistently lower at Helshoogte, the cooler terroir, compared to Papegaaiberg, the
warmer terroir. At flowering, Ψl was lower for grapevines at Helshoogte than at
Papegaaiberg, showing that diurnal grapevine water status was primarily controlled
by soil water content. The difference in grapevine water status between the two
terroirs gradually diminished until it was reversed during the post harvest period when
Ψl in grapevines at Papegaaiberg tended to be lower compared to those at
Helshoogte. The relatively low pre-dawn Ψl at Helshoogte indicated that the
grapevines were subjected to excessive water stress resulting from the low soil water
content. However, grapevines at Helshoogte did not suffer material water stress (i.e.
Ψl < -1.20 MPa) during the warmest part of the day, suggesting that partial stomatal
closure prevented the development of excessive water stress in the grapevines.
This suggests that low pre-dawn Ψl values do not necessarily imply that
grapevines will experience more water stress over the warmer part of the day, or visa
versa. This does not rule out the possibility that side-effects of partial stomatal closure, such as reduced photosynthesis, can have negative effects on grapevine
functioning in general. These results also suggest that measurement of diurnal Ψl
cycles at various phenological stages is required to understand and quantify terroir
effects on grapevine water status. / AFRIKAANSE OPSOMMING: Danksy die droogteweerstand van die wingerdstok is die verbouing van wingerde
sonder besproeiing ‘n praktiese en algemene verskynsel in die winterreënval-areas
van Suid-Afrika. Wynkwaliteit word grootliks bepaal deur die kwaliteit van die druiwe
waarvan dit gemaak word. Wingerdfisiologie word direk en indirek beïnvloed deur
waterstres, wat kan varieer volgens die grondtipe en die heersende atmosferiese
toestande. Die waterstatus van die wingerdstok beïnvloed druifsamestelling, direk of
indirek, en positief of negatief, afhangend van die graad en tydsduur van die
waterstres. Daar is drie belangrike faktore betrokke by die ontwikkeling van
waterstres, naamlik die transpirasietempo, die tempo van waterbeweging vanaf die
grond na die wortels, en die verhouding tussen die grondwatermatrikspotensiaal tot
blaarwaterpotensiaal. Al drie die faktore word beïnvloed deur die atmosferiese en/of
grondtoestande.
In warm wynboulande soos Suid-Afrika (Weskaap), met ‘n meditereense klimaat
wat gekarakteriseer word deur ‘n warm, droë somerperiode, is die belangrikste
eienskap van grond die vermoë om voldoende water aan die wingerdstok te verskaf
gedurende die hele seisoen. Blaarwaterpotensiaal (Ψl) het wye aanvaarding bekom
as die fundamentele meting van wingerstokwaterstatus, en word wyd toegepas in
wingerdkundige navorsing. Kort voor sonsopkoms, nader Ψl ‘n ewewig met die
grondwatermatrikspotensiaal en bereik ‘n maksimum daaglikse waarde.
Die studie vorm ‘n integrale deel van ‘n omvattende, multi-dissiplinêre
navorsingsprojek (ARC Infruitec-Nietvoorbij Projek No. WW13/01) op die effek van
grond en klimaat op wynkwaliteit, wat in 1993 in aanvang geneem het en in 2004
afgehandel sal word. Hierdie studie is uitgevoer gedurende die 2002/03 seisoen in
twee Sauvignon blanc wingerde geleë by Helshoogte en Papegaaiberg, beide in die
Stellenbosch distrik, ongeveer nege kilometer van mekaar. Twee eksperimentele
persele, elkeen verteenwoordigend van kontrasterende grondtipes in terme van
grondwaterregime, is geselekteer in elke wingerd. By Helshoogte word die twee
gronde verteenwoordig deur die Tukulu en Hutton grondvorms, en die gronde by
Papegaaiberg is van die Avalon en Tukulu vorms.
Die doel van die studie was om die effek van atmosferiese toestande en
grondwaterstatus op die wingerdstok se waterstatus vir elke grond by die twee
lokaliteite te bepaal, sowel as die effek van die wingerdstok se waterstatus op die
opbrengs en wynkwaliteit. Dit is gedoen deur die grondwaterstatus, die
grondwaterhouvermoë, sowel as die evapotranspirasie van die wingerdstokke op die
twee verskillende gronde by elk van die twee lokaliteite, wat verskil in mesoklimaat
en topografie, te bepaal en vergelyk. Die atmosferiese toestande by die twee
lokaliteite gedurende die 2002/03 seisoen is ook bepaal en vergelyk met die langtermyn gemiddelde atmosferiese toestande. Die vlakke van waterstres in
wingerdstokke op elke grond by elke lokaliteit is ook gemeet.
Gedurende die 2002/03 groeiseisoen, was die atmosferiese toestande relatief
warm en droog in vergelyking met die langtermyn gemiddeldes van vorige seisoene.
Hierdie kondisies aksentueer die effek van sekere grondeienskappe wat nie
noodwendig na vore kom gedurende normale, natter seisoene nie.
Die gewoonlike nat Tukulu grond by Helshoogte was droër as verwag gedurende
2002/03 in vergelyking met die Hutton grond. As gevolg van sterker groekrag op die
Tukulu grond, het wingerdstokke meer grondwater onttrek vroeg in die seisoen, wat
gelei het tot ‘n lae grondwatermatrikspotensiaal en meer waterstres in die
wingerdstokke. Die sterker groeikrag het meer beskaduwing van die lower asook
meer waterstres veroorsaak, wat gelei het daartoe dat die dominante aroma in wyne
vanaf druiwe op die Tukulu grond vars vegetatief was. Die Hutton grond het
bestendig gebly in terme van opbrengs en wynkwaliteit in vergelyking met vorige
seisoene. Daarteenoor het die Tukulu grond ‘n hoër opbrengs gelewer, maar met laer
as gewoonlike wynkwaliteit.
Die Avalon grond by Papegaaiberg het die hoogste grondwatermatrikspotensiaal
behou tot die einde van die seisoen, heelwaarskynlik a.g.v. kapillêre aanvulling
vanuit die ondergrond. Wingerdstokke op die Tukulu grond by Papegaaiberg het
heelwat meer waterstres ondervind as op die ander drie gronde, veral later in die
seisoen. Dit kan toegeskryf word aan ‘n kombinasie van faktore, die belangrikse
daarvan die erge grondkompaksie vlak in die grond, wat worteldiepte en
-verspreiding ernstig beperk het, wat op sy beurt nadelig is vir wingerdprestasie.
Beide die grondwaterstatus en atmosferiese toestande het ‘n belangrike rol
gespeel in die bepaling van die hoeveelheid waterstres wat die wingerdstok op
verskillende stadiums ondervind het. Die lugtemperatuur en waterdampdruktekort
was regdeur die seisoen laer by Helshoogte, die koeler terroir, as by Papegaaiberg,
die warmer terroir. Gedurende blom was die Ψl laer vir wingerdstokke by Helshoogte
as by Papegaaiberg, wat daarop wys dat daaglikse wingerdstok waterstatus
hoofsaaklik deur die grondwaterinhoud bepaal was. Die verskil in wingerdstok
waterstatus tussen die twee terroirs het geleidelik verminder totdat dit omgekeer was
gedurende die na-oes periode toe Ψl in wingerdstokke by Papegaaiberg geneig het
om laer te wees in vergelyking met die by Helshoogte. Die relatiewe lae voorsonop Ψl
by Helshoogte het daarop gedui dat die wingerdstokke aan oormatige waterstres
onderwerp was. Die wingerdstokke by Helshoogte het egter nie materiële waterstres
(i.e. Ψl < -1.20 MPa) gedurende die warmste gedeelte van die dag ondervind nie, wat
aandui dat gedeeltelike huidmondjiesluiting plaasgevind het om die ontwikkeling van
oormatige waterstres te verhoed.Dit dui aan dat lae voorsonop Ψl waardes nie noodwendig impliseer dat
wingerdstokke meer waterstres gedurende die warmste gedeelte van die dag sal
ondervind nie, of visa versa. Dit sluit nie die moontlikheid uit dat negatiewe neweeffekte
van gedeeltelike huidmondjiesluiting, soos ‘n vermindering in fotosintese, ‘n
negatiewe effek kan hê op die wingerdstok se funksionering in die algemeen nie.
Hierdie resultate stel voor dat die meting van daaglikse Ψl siklusse gedurende
verskeie fenologiese stadia benodig word om die effek van terroir op die wingerdstok
se waterstatus te verstaan en te kwantifiseer.
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16 |
The effect of exogenous protease on the relative enzyme activity of β-glucosidase in oenological conditionsSwart, Elsa Marita 12 1900 (has links)
Thesis (MScAgric)--University of Stellenbosch, 2004. / ENGLISH ABSTRACT: The distinctive varietal flavour of wines is a combination of absolute and relative
concentrations of chemical compounds. Volatile compounds are responsible for the
odour of wine and non-volatiles cause the sensation of flavour. Accompanying these
senses, a third, tactile, sense of ‘mouth-feel’ is recognizable. This forms the complete
organoleptic quality of wine.
Several hundred different compounds are simultaneously responsible for the
odour release in wine, and since there is no real character impact compound, the
aroma of wine can be described as a delicate balance of all these compounds. One
of the most important groups of volatiles is the monoterpenes, which play a role in
both aroma and flavour. This is especially significant for the Muscat varieties, but
these flavour compounds are also present in other non-muscat grape varieties,
where they supplement the varietal aroma. Monoterpenes occur in wine as free,
volatile and odorous molecules, as well as flavourless non-volatile glycosidic
complexes. The latter slowly releases monoterpenes by acidic hydrolysis, but the
impact on varietal aroma is considered insufficient for wines that are consumed
young. It is therefore important to supplement the release mechanism, in order to
enhance the varietal aroma of the wine. The enzymatic hydrolysis mechanism
functions in two successive steps: firstly, depending on the precursor, the glycosidic
linkage is cleaved by α-L-arabinofuranosidase, α-L-rhamnosidase, β-D-xylosidase or
β-D-apiosidase. The second step involves the liberation of the monoterpene alcohol
by a β-glucosidase. This enzymatic hydrolysis does not influence the intrinsic
aromatic characteristics of the wine, as opposed to acid hydrolysis.
Pectolytic enzymes play an important role in cell elongation, softening of tissue
and decomposition of plant material. These enzymes are used to improve juice
yields, release colour and flavour compounds from grape skins, as well as improve
clarification and filterability. Pectolytic enzymes work synergistically to break down
pectins in wine. Protopectinase produce water-soluble and highly polymerised pectin
substances from protopectin, it acts on non-methylated galacturonic acid units. Pectin
methylesterase split methyl ester groups from the polygalacturonic chain.
Polygalacturonase break down the glycosidic links between galacturonic acid units.
Pectin and pectate lyases have a β-eliminative attack on the chain and it results in
the formation of a double bond between C4 and C5 in the terminal residues.
From the above it can be seen that enzymes play a pivotal role in the
winemaking process. Unfortunately, in winemaking a lot of factors can influence the
effects of enzymes. One possible factor in the wine medium is the presence of acidprotease,
from yeast and/or fungal origin. This type of enzyme utilizes other enzymes
as substrates and renders them useless. Pure enzyme preparations were used to
study the interactions of a yeast acid-protease and a report activity (β-glucosidase) in
vitro. A bottled wine and a buffer were used as in vitro conditions. Enzyme assays were performed to determine the relative activity over a number of days. The results
indicated that even though both enzymes showed activity in both the media, the
yeast protease did not have any significantly affect on the report activity.
Subsequently wine was made from Sauvignon blanc grapes, with varying enzyme
preparation additions. Enzyme assays were performed during the fermentation; and
chemical, as well as sensory analysis were done on the stabilized wine. The results
confirmed that the yeast protease did not have any significant affect on the report
activity in these conditions. The protease’s inability to affect the report activity seems
unlikely due to the fact that it is active at a low pH range and has been suggested as
the only protease to survive the fermentation process. It seems possible that a winerelated
factor, possibly ethanol, is responsible. Thus it seems that yeast protease
does not threaten the use of commercial enzymes in the winemaking process in any
significant way.
Future work would entail more detailed enzyme studies of interactions
between protease, both from yeast and fungal origin, and other report activities in
specified conditions. The degradation capability could be directed towards unwanted
enzyme activities that cause oxidation and browning of the must. The
characterization of interactions between protease and β-glucosidase activities may
hold key to producing wines with enhanced aroma and colour potential, as well as
the elimination of unwanted enzyme activities. / AFRIKAANSE OPSOMMING: Die herkenbare kultivar karakter van wyn is ‘n kombinasie van absolute en relatiewe
konsentrasies van verskeie chemiese komponente. Vlugtige komponente is
verantwoordelik vir die geur, of aroma, van wyn en die nie-vlugtige komponente
veroorsaak die sensasie van smaak. ‘n Derde, fisiese sensasie, die ‘mondgevoel’, is
ook herkenbaar. Dit vorm die omvattende organoleptiese kwaliteit van die wyn.
‘n Paar honderd verskillende komponente is gelyktydig verantwoordelik vir die
aroma vrystelling in wyn en omdat daar geen werklike karakter ‘impak’ komponent is
nie, kan die aroma van wyn beskryf word as ‘n delikate balans van al die betrokke
komponente. Een van die mees belangrike groepe vlugtige komponente is die
monoterpene wat ‘n rol speel in beide aroma en smaak. Dit is veral belangrik by
Muskaat kultivars, maar hierdie aroma komponente is ook teenwoordig in niemuskaat
druif kultivars, waar hulle bydra tot die kultivar karakter en aroma.
Monoterpene kom in wyn voor as vry, vlugtige en aromatiese molekules en in
geurlose, nie-vlugtige glikosidies-gebonde komplekse. Die gebonde vorm word stadig
vrygestel deur ‘n suurhidrolise, maar dit word as onvoldoende beskou vir wyne wat
vroeg gedrink word. Dit is dus belangrik dat die vrystelling van geurstowwe verhoog
word om die kultivar karakter van die wyn te versterk. Die ensiematiese hidrolise
proses behels twee opeenvolgende stappe: eerstens, afhangende van die aard van
die voorloper, word die glikosidiese verbinding deur α-L-arabinofuranosidase, α-Lramnosidase,
β-D-xilosidase, of β-D-apiosidase gebreek. In die tweede stap word die
monoterpeen-alkohol deur β-glukosidase vrygestel. Hierdie ensiematiese afbraak
proses verander nie die intrinsieke aromatiese kenmerke van die wyn, soos met
suurhidrolise die geval is nie.
Pektolitiese ensieme speel ‘n fundamentele rol in selverlenging, sagwording en
afbraak van plant materiaal. Hierdie ensieme word gebruik om sap opbrengs te
verhoog, aroma en smaak komponente vry te stel uit die doppe, asook om
sapverheldering en filtrasie te verbeter. Die pektolitiese ensieme werk op ‘n
sinergistiese wyse om pektien in wyn af te breek. Protopektinase produseer wateroplosbare
en hoogs gepolimeriseerde pektien uit protopektien, slegs uit niegemetileerde
galakturoonsuur eenhede. Pektien metielesterase verwyder metielester
groepe van die poligalakturoonsuurketting. Die glikosidiese bindings tussen
galakturoonsuur eenhede word deur poligalakturonase afgebreek. Pektien- en
pektaat-liase het ‘n β-eliminasie aanslag op die ketting en as gevolg daarvan word
dubbelbindings tussen C4 en C5 in die terminale residue gevorm.
Vanuit bogenoemde is dit dus duidelik dat ensieme ‘n kardinale rol speel in die
wynbereidingsproses. Ongelukkig is daar ‘n verskeidenhied van faktore wat die
werking van ensieme in die wynbereidingsproses kan beïnvloed. Een moontlike
faktor is die teenwoordigheid van ‘n suur-protease, van fungisidiese en/of gis
oorsprong, in die wynmedium, omdat dit ander ensieme as substraat kan benut en degradeer. Suiwer ensiem preparate is gebruik om die ensiem interaksie tussen ‘n
gis suur-protease en ‘n verslag aktiwiteit (β-glukosidase) in vitro te ondersoek. ‘n
Gebotteleerde wyn en ‘n buffer is gebruik om die in vitro kondisies na te boots.
Relatiewe ensiem aktiwiteit is ontleed oor ‘n aantal dae. Beide die ensieme het
aktiwiteit getoon in die media, maar gis protease het geen statisties beduidende
invloed gehad op die aktiwiteit van die verslag ensiem nie. Daaropvolgend is wyn
berei van Sauvignon blanc druiwe, met verskillende ensiempreparaat toevoegings.
Die ensiemaktiwiteit is deurlopend tydens fermentasie gemeet. Na afloop van
stabilisasie is chemiese, sowel as sensoriese ontledings op die wyn gedoen. Die
resultate het bevestig dat gis protease, onder hierdie kondisies, geen beduidende
invloed op die verslag aktiwiteit gehad het nie. Die protease se onvermoë om die
verslag aktiwiteit beduidend te beinvloed blyk onwaarskynlik aangesien die suurprotease
aktief is by lae pH vlakke en dit as die enigste protease voorgestel is wat
die fermentasie proses kan oorleef. Dit blyk asof ‘n wyn-verwante faktor, moontlik
etanol, hiervoor verantwoordelik kan wees. Dus hou protease geen gevaar in vir die
gebruik van kommersiële ensieme in wynbereiding nie.
Navorsing kan in die toekoms fokus op meer gedetailleerde ensiem interaksie
studies tussen protease en ander ensiem aktiwiteite, in gespesifiseerde kondisies.
Die degradasie kapasiteit kan moontlik aangewend word om ongewenste ensiem
aktiwiteite, wat byvoorbeeld oksidasie en verbruining veroorsaak, te verminder. Die
karakterisering van die interaksies tussen protease en β-glukosidase kan dus die
sleutel wees tot die produksie van wyne met verhoogde aroma potensiaal, asook die
eliminasie van ongewenste ensiematiese aktiwiteite.
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The endopolygalacturonases from Botrytis cinerea and their interaction with an inhibitor from grapevineWentzel, Lizelle 04 1900 (has links)
Thesis (MSc)--University of Stellenbosch, 2005. / ENGLISH ABSTRACT: In the field of agriculture, plant pathogens are a major concern because of the severe damage these organisms cause to crops yearly. Fundamental studies regarding plant pathogens and their modes of action made it possible for researchers in the field of molecular biology to investigate pathogens further on a molecular level. Botrytis cinerea, has been used to great effect as a model system to investigate various aspects regarding pathogenesis, also on a molecular level.
Molecular research done on B. cinerea over the last few years has shown that the endopolygalacturonases (EPGs) of this fungus are key role players in pathogenesis. This hydrolytic enzyme family of six members, encoded by the Bcpg1-6 genes, are important in breaking down the complex cell wall polymers of host plants, enabling the fungus to penetrate its host sufficiently. It has been shown that both BcPG1 and 2 are crucial for virulence of B. cinerea. A leucine-rich repeat inhibitor protein situated in the cell wall of various plant species, the polygalacturonase-inhibiting protein (PGIP), has been proven to interact with and inhibit EPGs, and thus the necrotic actions of B. cinerea. From literature it was clear that specific data regarding individual interactions of fungal EPGs with PGIPs are lacking currently. Furthermore, most experiments regarding the effects of EPG as well as interaction and inhibition studies of EPGs and PGIPs, rely on in vitro methods, without the possibility to contextualize the results on an in vivo or in planta level. The scope of this study was to specifically address the issues of individual EPG:PGIP interactions and the use of possible in vivo methodology by using EPGs from a highly virulent South African strain of B. cinerea and the grapevine VvPGIP1 that has been previously isolated in our laboratory. This PGIP, originally isolated from Vitis vinifera cv Pinotage, has been shown to inhibit a crude EPG extract from this strain with great efficiency. The approach taken relied on heterologous over-expression of the individual Bcpg genes and the isolation of pure and active enzymes to evaluate the inhibition of the EPGs with VvPGIP1. The genes were all successfully over-expressed in Saccharomyces cerevisiae with a strong and inducible promoter, but active enzyme preparations have been obtained only for the encoding Bcpg2 gene, as measured with an agarose diffusion assay. The in vitro PGIP inhibition assay is also based on the agarose diffusion assay and relies on activity of the EPGs to visualize the inhibiting effect of the PGIP being tested. The active EPG2, however, was not inhibited by VvPGIP1 when tested with this assay. The EPG encoding genes from B. cinerea were transiently over-expressed also in Nicotiana benthamiana by using the Agrobacterium-infiltration technique. Transgene expression was confirmed by Northern blot analysis and EPG-related symptoms were observed five to eight days post-infiltration. Differential symptoms appeared with the various EPGs, providing some evidence that the symptoms were not random events due to the infiltration or a hypersensitive response. Moreover, the symptoms observed for EPG2 was similar to those that were reported recently by another group on the same host. In spite of the expression data and the clear symptoms that developed, active preparations, as measured with the agarose diffusion plate asay, could only be obtained for EPG2 again.
In our search for a possible in vivo method to detect and quantify EPG activity and inhibition by PGIPs, we tested and evaluated a technique based on chlorophyll fluorescence to detect the effect of EPGs on the rate of photosynthesis. Our results showed that the over-expression of these genes reduced the rate of electrons flowing through photosystem II, indicating metabolic stress occurring in the plant. We used the same technique to evaluate possible interaction between VvPGIP1 respectively with BcPG1 and 2 and found that the co-expressing of the Vvpgip1 gene caused protection of the infiltrated tissue, indicating inhibition of EPG1 and 2 by VvPGIP1. For EPG2, the observed interaction and possible inhibition by VvPGIP1 is the first report to our knowledge of an interaction between this specific EPG2 and a PGIP. Moreover, to further elucidate the in planta interaction between VvPGIP1 and the EPGs from the South African B. cinerea strain, we tested for possible interactions by making use of a plant two-hybrid fusion assay, but the results are inconclusive at this stage.
Previous studies in our laboratory have shown that several natural mutations exist between PGIP encoding genes from different V. vinifera cultivars. Based on this finding and the fact that these natural mutations could result in changes with regard to EPG inhibition and ultimately disease susceptibility, we isolated an additional 37 PGIP encoding genes from various grapevine genotypes, some of which are known for their resistance to pathogens.
Combined, these results make a valuable contribution to understand plant pathogen interactions, specifically in this case by modeling the interactions of pathogen and plant derived proteins. The possibility to use in vivo methods such as chlorophyll fluorescence to follow these interactions on an in planta level, provides exciting possibilities to strenghten and contextualize in vitro results. / AFRIKAANSE OPSOMMING: Plantpatogene organismes veroorsaak jaarliks erge skade aan landbougewasse en word dus as ’n ernstige probleem in die landbousektor beskou. Diepgaande studies wat handel oor plantpatogene en hul metodes van infeksie het dit vir molekulêre bioloë moontlik gemaak om patogene nou ook op molekulêre vlak verder te bestudeer. Botrytis cinerea is baie effektief as modelsisteem gebruik om verskeie aspekte van patogenese verder te bestudeer, ook op ‘n molekulêre vlak.
Molekulêre navorsing op B. cinerea, het getoon dat die endopoligalakturonases (EPGs) van dié swam kernrolbelangrik in patogenese is. Hierdie sesledige hidrolitiese ensiemfamilie word gekodeer deur die Bcpg1-6 gene en is belangrik vir die afbraak van die komplekse selwandpolimere van plantgashere, om suksesvolle gasheerpenetrasie te veroorsaak. Daar is aangetoon dat beide BcPG1 en 2 essensieël vir virulensie van die patogeen is. ’n Leusienryke-herhalings inhibitorproteïen wat in die selwand van verskeie plantspesies voorkom, die poligalakturonase-inhiberende proteïen (PGIP), het interaksie met en inhibeer EPGs en gevolglik ook die nekrotiserende aksies van B. cinerea. Uit die literatuur is dit duidelik dat spesifieke inligting aangaande individuele interaksies van fungiese EPGs met PGIPs tans nog ontbreek. Verder word daar op in vitro metodologie staatgemaak wannneer die effekte van EPGs asook die interaksie en inhibisie met PGIPs bestudeer word, sonder om die konteks van die in vivo- of in planta-omgewing in ag te neem. Die fokus van hierdie studie was om aspekte van individuele EPG:PGIP interaksies, asook die moontlike gebruik van in vivo metodologie te bestudeer deur EPGs, afkomstig van ’n hoogs virulente Suid-Afrikaanse ras van B. cinerea en die wingerd VvPGIP1, wat vroeër in ons laboratorium geïsoleer is, te gebrruik. Hierdie PGIP wat uit Vitis vinifera cv Pinotage geïsoleer is, inhibeer ’n kru EPG-ekstrak van bogenoemde ras baie effektief. Die benadering wat gevolg is het op die ooruitdrukking van die individuele Bcpg-gene in heteroloë sisteme staatgemaak en die gevolglike isolering van suiwer en aktiewe ensieme om EPG-inhibisie deur VvPGIP1 te beoordeel. Al die gene is suksesvol in Saccharomyces cerevisiae ooruitgedruk onder ’n sterk induseerbare promotor, maar volgens ’n agarose-diffundeerbare toets kon aktiewe ensiempreparate slegs vir die enkoderende Bcpg2 verkry word. Die in vitro PGIP-inhibisie toets is ook op die gemelde toets gebasseer en vereis EPG-aktiwiteit om die inhiberende effek van die PGIP, te visualiseer. Die aktiewe EPG2 is egter nie deur VvPGIP1 geïnhibeer met die aanleg van hierdie toets nie. Die EPG-enkoderende gene van B. cinerea is ook tydelik in Nicotiana benthamiana ooruitgedruk deur gebruik te maak van ’n Agrobacterium-infiltrasietegniek. Transgeenuitdrukking kon met die Noordelike kladtegniek bevestig word en EPG-verwante simptome is vyf tot agt dae na infiltrasie waargeneem. Verskillende simptome vir die verskillende EPGs is waargeneem, wat aanduidend is dat die simptome nie lukrake gevolge van die infiltrasies, of ’n hipersensitiewe respons is nie. Verder kon die simptome wat EPG2 vertoon het, gekorreleer word met dié wat onlangs deur ’n ander groep op dieselfde gasheer waargeneem is. Ten spyte van die ekspressiedata en die waargenome simptome, kon aktiewe ensiempreparate op die agarose-diffundeerbare toets, weereens slegs vir EPG2 waargeneem word.
’n Metode wat gebasseer is op chlorofilfluoressensie is getoets en geëvalueer as ’n moontlike in vivo metode om EPG aktiwiteit en inhibisie deur PGIPs waar te neem en te kwantifiseer. Die resultate het bevestig dat die ooruitdrukking van hierdie gene die elektronvloeitempo deur fotosisteem II verminder het wat ’n aanduiding is dat metaboliese stres in die plant heers. Dieselfde tegniek is gebruik om die moontlike interaksies tussen BcPG1 en 2 en VvPGIP1 te bestudeer en het aangetoon dat die mede-uitdrukking van die Vvpgip1-geen aanleiding gee tot ’n beskermende effek van die geinfiltreerde weefsel, wat aanduidend is van inhibisie van EPG1 en 2 deur VvPGIP1. In die geval van EPG2 is hierdie interaksie en moontlike inhibisie met ’n PGIP die eerste waarneming in die verband. In ’n verdere poging om die in planta-interaksie tussen VvPGIP1 en die EPGs van die Suid-Afrikaanse B. cinerea ras uit te klaar, is ’n plantgebasseerde twee-hibriede toets aangelê, maar geen klinkklare resultate kon verkry word nie.
Vorige werk het bevestig dat verskeie natuurlike mutasies in PGIP-enkoderende gene, afkomstig van verskillende V. vinifera kultivars, voorkom. Hierdie resultaat en die feit dat hierdie mutasies verskille in EPG inhibisie en uiteindelik vatbaarheid vir siektes kan beïnvloed, het aanleiding gegee tot die isolering van ’n verdere 37 PGIP-enkoderende gene uit ‘n verskeidenheid druifplantgenotipes, sommige waarvan juis bekend vir hul weerstand teen patogene is.
Die gekombineerde resultate wat in dié studie verkry is, maak ’n waardevolle bydrae tot die verstaan van plant-patogeeninteraksies, spesifiek met die modelering van interaksies van patogeen- en plantgebasseerde proteïene. Die moontlikheid om in vivo-metodes soos chlorofilfluoressensie te gebruik in in planta-analises, is besonder bemoedigend om in vitro-resultate te versterk en ook in konteks te plaas.
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A study of the interaction between vine vigour, crop level and harvest dates and their effects on grape and wine characteristicsQuixley, Pieter C 03 1900 (has links)
Thesis (MscAgric (Viticulture and Oenology))--University of Stellenbosch, 2007. / A common phenomenon in most South African vineyards, especially in the Western
Cape region, is that of within vineyard variation. This variation phenomenon is caused
by an array of controllable and non-controllable factors that interact with each other to
affect vine vigour. Controllable factors can be managed by the grape grower, while the
non-controllable factors have to be managed in the planning process in order not to
negatively affect productivity or product quality.
The main goal of any grape grower is to optimise vine performance in an attempt to
achieve the best possible yield while at the same time allowing vines to optimally ripen
grapes towards optimal wine quality. A grape grower has to use every possible means
and technique available to him in order to manage his vineyards in such a manner as to
achieve this goal. In the past, it was difficult to visualize the extent and distribution of
vigour variation in vineyards, but with modern technological improvements in the field of
remote sensing, grape growers are able to identify and specify different vigour levels
within a vineyard.
When remote sensing is applied in a vineyard, the grape grower can identify certain
areas that may need more specific attention than others. Consequently, managerial
decisions based on detailed information can be made in an attempt to improve the
general condition and performance of a vine. Not only can the acquired information be
used to plan managerial actions throughout the season, but it can also be used to plan
and devise harvest strategies. Some areas in a vineyard may be at a certain point in the
ripening process and need to be harvested, while grapes from other areas still need to
develop the wanted flavours. One managerial action applied at véraison by some grape
growers, is that of crop thinning. Different vigour areas can now be subjected to various
crop thinning actions in an attempt to determine the best crop load for a vigour level.
With this in mind, two studies were launched to firstly investigate the interaction
between vine vigour and harvest dates; and secondly to investigate the interaction
between vine vigour and crop load and how their combined interaction might influence a
vine’s characteristics, grape composition and wine quality. Vigour variation was firstly
identified through multispectral aerial imagery, and then visually verified by visits to the
experimental vineyards. The multispectral aerial image was then “orthorectified” in order
to produce a classified multispectral image. The image was classified through different
colour codes that were assigned to the different vigour levels to clearly distinguish
between them. A series of vegetative and reproductive measurements were conducted
to try and establish if any correlations could be obtained of the interaction between vine
vigour, different harvest dates and crop loads. In order to verify differences in vine
vigour, underlying causes were also determined through soil analyses of which
chemical analysis, bulk density, porosity, as well as root penetration and distribution
were determined. Vegetative measurements that were conducted for both studies
indicated good correlations between the different vigour levels and the image
classifications. The results also identified the effect that topping (mechanical or manual) had on the main and lateral leaf areas. Reproductive measurements throughout the
season, in the form of berry sampling, showed changes in berry composition and
accentuated the effects of the different treatments, which could also be confirmed
through sensorial analysis of the wines. The results also emphasized the need to not
only make use of one of two chemical parameters to identify grape ripeness, but to
incorporate a number of parameters, such as sugar, pH and acid levels. From the
varying grape chemical characteristics, a wine style can be identified that might carry
the approval of the winemaker for the production of a specific type of wine. Soil studies
of both vineyards also gave important evidence for the causes of vigour variation.
The data collected will hopefully provide grape growers with information that will
enable them to make educated decisions concerning grape production and how vigour,
in conjunction with different harvest dates and crop loads, will enable them to produce
fruit of good quality and, so doing, improve their financial position.
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Grapevine (Shiraz/Richter 99) water relations during berry ripeningEllis, Warren 03 1900 (has links)
Thesis (MscAgric (Viticulture and Oenology))--Stellenbosch University, 2008. / The effect of various irrigation strategies on grapevine water relations during the
berry ripening period was investigated in a Shiraz/Richter 99 vineyard. Comparisons
between different irrigation strategies (full/seasonal, véraison+post véraison, post
véraison and no irrigation) were made.
During the day, the seasonally irrigated vines experienced less water stress than the
deficit treatments. Non-irrigated vines seemed to maintain higher diurnal leaf water
potentials. Lower leaf water potentials indicated lower water contents in the
vegetative and reproductive tissue. Full irrigation seemed to stimulate primary shoot
length. Longer water deficit induced earlier and more complete shoot maturation
(reserve accumulation). Re-distribution of leaf area on the shoot may occur when
vines are subjected to water deficit. Extended water deficit seemed to induce earlier and restricted water loss from vegetative tissue. The water relations were reflected in the berry size. Irrigation during ripening seemed to induce a continuation of berry water loss. Transpiration losses were apparently much higher in fully irrigated vines
whereas stomatal control efficiently maintained water relations in non-irrigated vines. Water deficit seemed to have enhanced the soluble solid accumulation. Irrigation
treatments did not seem to affect the titratable acid and pH. The post véraison
irrigation in particular seemed to favour a wide window for harvesting. Irrigation at
post véraison and especially véraison+post veraison seemed to have a greater effect
on the synthesis and extraction of phenolics, anthocyanins and tannins in the berry skins. Different irrigation strategies may affect grapes in such a way that different wine styles are obtained.
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Evaluating the effect of different winemaking techniques on ethanol productionBiyela, Busisiwe Nokukhanya E. 12 1900 (has links)
Thesis (MscAgric (Viticulture and Oenology))--Stellenbosch University, 2008. / Over the years, different techniques have been used to legally reduce the ethanol content of
wines. Several physical processes are available for producing wines with less alcohol. Despite
their efficacy, these treatments have a capital and operational cost influence. They can also
affect the concentration of other wine components. On the other hand, vast amount of research
has been conducted through genetic modification of wine yeast strains in order to reduce the
ethanol yield of Saccharomyces cerevisiae by diverting sugar metabolism towards various byproducts.
However, genetically modified yeasts are not currently accepted in most wine
industries worldwide, including South Africa. Therefore, other approaches need to be
envisaged.
Commercial enzymes are commonly added during winemaking. Most enzymes essential for
vinification naturally occur in grapes, but are inefficient under pH and sulphur levels associated
with winemaking. Enzymes of fungal origin are resistant to such conditions. The most widely
used commercial enzymes include pectinases, hemicellulases, glucanases and glycosidases.
With the exception of glucanases, produced by Trichoderma harzianium, all the other enzymes
are produced by Aspergillus niger.
In this study, the possibility of using Gluzyme Mono® 10.000 BG (Gluzyme) (Novozymes,
South Africa) to reduce the glucose content of synthetic grape must and grape must before
fermentation in order to produce wine with a reduced alcohol content was investigated.
Gluzyme is a glucose oxidase preparation from Aspergillus oryzae, currently being used in the
baking industry. Glucose oxidase catalyses the oxidation of glucose to gluconic acid and
hydrogen peroxide in the presence of molecular oxygen.
Gluzyme was initially used in synthetic grape must where different enzyme concentrations
and factors influencing its activity were investigated for its use in winemaking. The results
showed that up to 0.5% v/v less alcohol were obtained using an enzyme concentration of 20 kU
compared to the control. This reduction in alcohol was increased to 1 and 1.3% v/v alcohol at
pH 3.5 and pH 5.5 respectively in aerated synthetic grape must using 30 kU enzyme.
Secondly, Gluzyme trials were carried out using Pinotage grape must. Gluzyme treated
wines after fermentation contained 0.68% v/v less alcohol than the control samples at 30 kU
enzyme. Colour and volatile flavour compounds of treated wine did not differ significantly from
the untreated samples. Lower free anthocyanin and total phenol concentrations in treated than
control samples were observed, possibly due to the hydrogen peroxide oxidation which could
have led to polymerisation.
The present study has clearly demonstrated that Gluzyme may be used in winemaking to
produce reduced-alcohol wine without affecting its colour and aroma compounds. The enzyme
in its current form is however, not ideal for winemaking; other forms such as liquid or powder
form should be considered if the enzyme is to be used under winemaking conditions.
Future work should focus on evaluating the potential new form of the enzyme and studying
the effects of Gluzyme in various grape must in semi-industrial scale. A tasting panel should
also evaluate its impact on the organoleptic properties and the overall quality of the resulting wines.
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